The turnover of ketone bodies and acetate was evaluated as well from the disappearance rate of (3-14C)acetoacetate or (1-14C)acetate respectively as from the conversion of FFA into these metabolites in normal weight and obese overnight-fasted and in obese long-term starved patients. The disappearance rate of (1-14C)oleate was the same in all three groups. Long-term starvation enhanced ketone body turn-over almost 10-fold, whereas the disappearance rate for ketone bodies decreased from 0.035 to 0.015 min-1. Under the same circumstances the turnover of acetate was about 1 mumol g-1 min-1 accounting for about 5% of FFA turnover. Long-term starvation decreased the conversion of (1-14C)oleate into triglycerides by almost 50% and increased the (2-C)-(4-C)/(1-C) ratio of radioactivity in ketone bodies. The reincorporation of radioactivity from the (1-C)position of (1-14C)oleate into the ( (2-C)-(n-C) ) position of FFA, which is a measure of the reutilization of acetyl-CoA for FFA synthesis decreased significantly during long-term starvation.